1. Field of the Invention
The present invention generally relates to detector efficiency measurement and more specifically, to an infrared focal plane array (FPA) crosstalk measurement system and technique.
2. Description of Prior Art
Crosstalk occurring in a FPA imaging system will degrade the system Modulation Transfer Function (MTF) thereby lowering the overall system performance. Optical crosstalk occurs due to the effects of optical reflections, refractions, scattering, internal and external to the FPA. Electrical crosstalk can be attributed to factors such as the charge transfer inefficient of the charge couple device (CCD), or the incomplete discharge of a detector's integration capacitance. A maximum allowable crosstalk is now specified for all new U.S. Army FPA systems and is an important performance parameter that must be measured.
In the prior art, crosstalk measurement is achieved by using a small aperture blackbody source imaged onto the FPA using an off-axis parabolic collimating mirror coupled with a focussing lens. To measure crosstalk accurately it is essential that the spot size of the radiation source utilized be smaller than the detector size. In order to achieve a small spot size for an incoherent source, relatively expensive large optical elements are needed. The use of an incoherent source has thus led to limitations in crosstalk measurement due to the difficulty of forming a small spot size. While the prior art has reported using an incoherent source with mirror elements for crosstalk measurement none have established a basis for a specific apparatus that is dedicated to the task of resolving the particular problem at hand.
What is needed in this instance is a infrared FPA crosstalk measurement technique and system that utilizes a coherent radiation source.